Sandwich panels are well known in the industry, especially in the construction and transportation industry. Sandwich panels are laminated structures composed of alternating objects of different materials. Typically, sandwich panels comprise a core structure trapped between external structural sheets. Due to the versatility of materials used in the manufacturing of sandwich panels, efficient bonding solution is required.
In that context, two component epoxy adhesives have been widely used as bonding solution for manufacturing sandwich panels. However, due to its reactivity epoxy adhesives generally require high curing temperature and/or long pressing time, which are undesired in industrial production processes. Alternative bonding solutions using polyurethane adhesives, in particular two-component urethane adhesives have been used and are known to offer the advantage of an extended pot life at ambient temperature at the detriment of the curing time. In order to promote curing, these systems typically require a catalyst, typically an organometallic compound, such as e.g. catalysts based on organotin compounds or organobismuth compounds; or an amine or amine-like compound. Unfortunately however, the faster curing or conversion permitted by these catalysts is generally accompanied with shortening of the pot life.
Industrial processes of manufacturing sandwich panels typically require adhesive compositions providing long open time and minimal press time, while providing acceptable curing time. Polyurethane-based adhesives claimed to provide both long open times and rapid “on demand” curing are described in WO 95/08579 A1 (Schoener et al.) and in U.S. 2012/0301729 A1 (Schmider et al.). The disclosed systems do however require using complex catalytic and/or curing systems, which in turn will lead to cost-inefficient and complex production processes. Some systems also make use of recognized harmful materials such as tin- or bismuth-based compounds, requiring stringent CLP labeling.
Without contesting the technical advantages associated with the adhesive solutions known in the art, there is still a need for a stable and cost-effective adhesive composition providing long open time and low toxicity. Other advantages of the adhesive compositions and methods of the disclosure will be apparent from the following description.